An interference cancellation (IC) receiver improves reception performance by reconstructing or estimating one or more interfering signal components within a received signal, for use in suppressing the interfering component(s) with respect to one or more desired signal components within the received signal. The terms “interfering” and “desired” may be regarded as working labels because IC processing can be performed for a desired signal component with respect to one or more other signal components, desired or otherwise. Various IC receiver architectures are known.
One class or type of IC receiver uses post-decoding IC. Such receivers obtain a regenerated signal corresponding to a given interferer according to a signal regeneration process that commonly includes four steps: symbol estimate generation (e.g. by using equalization and/or Interference Rejection Combining or IRC); soft value extraction (e.g. using the “log-max” method or other soft-bit processing); decoding for soft value improvement (e.g. using a soft-output Turbo decoder); and soft value-to-soft symbol mapping, where such mapping is driven by decoded bits or related soft bit information.
The decoding step may be omitted in some scenarios and architectures, yielding a structure that may be referred to as a “pre-decoding” IC architecture. In such receivers, the initial soft bit values obtained for, e.g., interfering symbols, are immediately used for soft symbol mapping.
However, while relatively efficient approaches are known for the generation of soft symbol values from soft bit information, the complexity of these approaches is still far from negligible, especially for Higher Order Modulation (HOM). For example, for 64QAM, six soft values have to be generated per received symbol and a corresponding six terms added to form the soft symbol estimate, including related absolute value, addition, function lookup, and scaling operations. Furthermore, simplifications of the soft value extraction process that incorporate an implicit log-max approximation may suffer from poor performance at the low symbol SNR levels that are typical for other-cell interference signals within wireless communication networks, such as UTRAN and E-UTRAN based cellular communication networks.